Homoleptic complexes of cobalt(0) and nickel(0,I) with 1,1'-bis(diphenylphosphino)ferrocene (dppf): synthesis and characterization.

Reduction of Co(dppf)Cl2 with 2 equiv of sodium naphthalenide in THF, in the presence of dppf, affords the homoleptic complex Co(dppf)2, 1, isolated in 65% yield as a brick red solid, extremely air sensitive. In solution, under inert atmosphere, 1 slowly decomposes into Co and dppf, following a first-order kinetic law (t1/2 = 21 h at 22 degrees C). Similarly to the Rh and Ir congeners, 1 undergoes a one-electron reversible reduction to [Co(dppf)2]-. Attempts to obtain this d10 species by chemical as well as electrochemical reduction of 1 lead to the hydride HCo(dppf)2, 2, as the only product that can be isolated. Reduction of Ni(dppf)Cl2 with sodium in the presence of dppf and catalytic amounts of naphthalene affords Ni(dppf)2, 3, isolated in 60% yield as a yellow air stable solid. The stoichiometric oxidation of 3 with [FeCp2]PF6 forms the d9 complex [Ni(dppf)2]PF6, 4, which represents the second example of a structurally characterized Ni(I) complex stabilized by phosphines. A single-crystal X-ray analysis shows for the metal a distorted tetrahedral environment with a dihedral angle defined by the planes containing the atoms P(1), Ni, P(2) and P(3), Ni, P(4) of 78.2 degrees and remarkably long Ni-P bond distances (2.342(3)-2.394(3) A). The EPR spectroscopic properties of 1 (at 106 K in THF) and 4 (at 7 K in 2-methyl-THF) have been examined and g tensor values measured (1, gx = 2.008, gy = 2.182, gz = 2.326; 4, gx = 2.098, gy = 2.113, gz = 2.332). A linear dependence between the hyperfine constants and the Ni-P bond distances has been evidenced. Finally, the change with time of the EPR spectrum of 4 indicates that it very slowly releases dppf.

Gold dithiocarbamate derivatives as potential antineoplastic agents: design, spectroscopic properties, and in vitro antitumor activity.

At present, cisplatin (cis-diamminodichloroplatinum(II)) is one of the most largely employed anticancer drugs as it is effective in the treatment of 70-90% of testicular and, in combination with other drugs, of ovarian, small cell lung, bladder, brain, and breast tumors. Anyway, despite its high effectiveness, it exhibits some clinical problems related to its use in the curative therapy, such as a severe normal tissue toxicity (in particular, nephrotoxicity) and the frequent occurrence of initial and acquired resistance to the treatment. To obtain compounds with superior chemotherapeutic index in terms of increased bioavailability, higher cytotoxicity, and lower side effects than cisplatin, we report here on some gold(I) and gold(III) complexes with dithiocarbamate ligands (DMDT = N,N-dimethyldithiocarbamate; DMDTM = S-methyl-N,N-dimethyldithiocarbamate; ESDT = ethylsarcosinedithiocarbamate), which have been synthesized, purified, and characterized by means of elemental analyses, conductivity measurements, mono- and bidimensional NMR, FT-IR, and UV-vis spectroscopy, and thermal analyses. Moreover, the electrochemical properties of the designed compounds have been studied through cyclic voltammetry. All the synthesized gold complexes have been tested for their in vitro cytotoxic activity. Remarkably, most of them, in particular gold(III) derivatives of N,N-dimethyldithiocarbamate and ethylsarcosinedithiocarbamate, have been proved to be much more cytotoxic in vitro than cisplatin, with IC50 values about 1- to 4-fold lower than that of the reference drug, even toward human tumor cell lines intrinsically resistant to cisplatin itself. Moreover, they appeared to be much more cytotoxic also on the cisplatin-resistant cell lines, with activity levels comparable to those on the corresponding cisplatin-sensitive cell lines, ruling out the occurrence of cross-resistance phenomena and supporting the hypothesis of a different antitumor activity mechanism of action.

Iridium(III, 0, and -I) Complexes Stabilized by 1,1'-Bis(diphenylphosphino)ferrocene (dppf): Synthesis and Characterization. Crystal Structures of [Na(THF)(5)][Ir(dppf)(2)].THF and [Ir(dppf)(2)].

The iridium(I) complex stabilized by the organometallic ligand 1,1'-bis(diphenylphosphino)ferrocene (dppf), [Ir(dppf)(2)](+), 1, undergoes a cyclometalation reaction in solution to give the iridium(III) hydride [IrH(dppf(-H))(dppf)](+), 2, which has been isolated and characterized by spectroscopic methods. The compound is the final product of the intramolecular oxidative addition of the ortho C-H bond of a phenyl substituent of the diphosphine and is formed through an intermediate hydride, which has also been spectroscopically characterized. 1 can be electrochemically reduced to the Ir(0) and Ir(-I) species, [Ir(dppf)(2]), 3, and [Ir(dppf)(2)](-), 4, respectively, in two reversible single-electron processes. These low-valent metal complexes have been obtained by chemical reduction of 1 with sodium naphthalenide in tetrahydrofuran solution and their crystal and molecular structures determined by single-crystal X-ray analyses. 3 crystallizes in the triclinic system, space group P&onemacr;, with a = 13.019(4) Å, b = 13.765(6) Å, c = 15.549(5) Å, alpha = 93.74(3) degrees, beta = 90.35(3) degrees, gamma = 92.07(3) degrees, V = 2779(2) Å(3), and Z = 2. Anionic complex 4 crystallizes as sodium-solvated salt [Na(THF)(5)][Ir(dppf)(2)].THF, 4b, in which the sodium cation is surrounded by five molecules of THF in a slightly distorted trigonal-bipyramidal environment. 4b crystallizes in the monoclinic system, space group P2(1)/n, with a = 13.325(3) Å, b = 23.976(5) Å, c = 26.774(7) Å, beta = 98.77(2) degrees, V = 8454(4) Å(3), and Z = 4. The coordination geometry around the metal in neutral d(9) complex 3 is intermediate between the highly distorted square-planar geometry, found earlier in cationic d(8) species 1, and the almost regular tetrahedral arrangement of the two diphosphines in the anionic d(10) complex 4. Reduction of Ir(I) to Ir(0) and Ir(-I) causes a stepwise decrease of the Ir-P bond length of 0.04 Å (average) and 0.05 Å, respectively, with a concomitant increase of the bite angle of the diphosphine which ranges from 94.3 degrees (average) in [Ir(dppf)(2)](+) to 102.3 degrees in [Ir(dppf)(2)](-).